The origin and control of dimethyl sulphide and its precursor in malt.
Hysert, D.W., Weaver, R.L. and Morrison, N.M.
Dimethyl sulphide (DMS) and its precursor (DMSP) were determined in the same sample of malt in the following way. About 20 g of ground malt were extracted for 5 min with 100 ml of water at room temperature in a sealed centrifuge tube. After cooling to 0 degrees C and clarification, 20 ml of the supernatant were transferred to a Pierce Hypo-Vial and the DMS concentration determined by injection of 1.0 ml of the headspace gas into a GLC. 18 ml of the cold supernatant were mixed with 2 ml of 10N NaOH and boiled for 1 h to convert all the DMSP to DMS. Total DMS content of this treated sample was then measured as previously described. Neither DMS nor DMSP could be found in ungerminated barley. During germination DMSP increased steadily but free DMS did not appear. On kilning, DMSP declined and DMS became measurable for the first time in the process. Dissection of malt grains indicated that about half of the DMS and DMSP were present in the endosperm and the other half in the embryo, scutellum and acrospire combined. In relation to weight the acrospire was distinctly the richest tissue. Study of a number of commercial barleys and malts indicated that a wide variation in DMS and DMSP content occurs in practice. The major factors seemed to be (a) barley variety, with six rowed types always giving higher DMS and DMSP than two rowed types, (b) extent of modification, with the level of DMSP increasing with the degree of modification and (c) kilning, with both an increase in time or temperature leading to appreciable falls in DMSP. Although more extensively kilned malts tend to have higher DMS levels than the lightly kilned malts, this material tends to be lost during wort boiling.
Keywords: dimethyl sulphide malt malting sulphur compound volatile compound